Reservoirs formed with a flexible liner layed in or lining an earthen containment space, or lining a tank, are well known in the art. U.S. Pat. Nos. 3,872,007, 3,474,625 and 1,081,515 disclose various arrangements of formed reservoirs utilizing a flexible liner. However, these prior art reservoirs generally provide for the liner being a one piece affair, defining the entire containment space or reservoir, and have not been entirely satisfactory. Moreover, to applicant's knowledge, no one heretofore has provided a containment reservoir utilizing a flexible liner material, and having a covering layer of pervious fabric material overlying the opening into the reservoir, for filtering liquid passing into the reservoir, and as is disclosed in applicant's invention.